Inkjet printers are commonplace in homes and offices. More recently, inkjet printers have been proposed for use in portable devices, such as digital cameras, mobile phones etc. Furthermore, with the advent of MEMS technology, whereby inexpensive photolithographic techniques from the semiconductor industry are used to manufacture microelectomechanical systems, the possibility of disposable inkjet printers is becoming a commercial reality. The present Applicant has developed many different types of MEMS inkjet printheads, some of which are described in the patents and patent applications listed in the above cross reference list.
The contents of these patents and patent applications are incorporated herein by cross-reference in their entirety.
Although the cost and power requirements of inkjet printheads is being reduced through the use of MEMS technology and improved inkjet nozzle designs, it is also necessary to reduce the cost and power requirements of other printer components, in order to incorporate inkjet printers into portable devices or to provide disposable inkjet printers.
A crucial aspect of inkjet printing is maintaining the printhead in an operational printing condition throughout its lifetime. A number of factors may cause an inkjet printhead to become non-operational and it is important for any inkjet printer to include a strategy for preventing printhead failure and/or restoring the printhead to an operational printing condition in the event of failure. Printhead failure may be caused by, for example, printhead face flooding, dried-up nozzles (due to evaporation of water from the nozzles—a phenomenon known in the art as decap), or particulates fouling nozzles.
In some cases, printhead failure may be remedied by simply firing nozzles periodically using a ‘keep wet cycle’. This strategy does not require any external mechanical maintenance of the printhead and may be appropriate when a nozzle has not been fired for a relatively short period of time (e.g. less than 60 seconds). A ‘keep wet cycle’ can be used to address decap, and the consequent formation of viscous plugs in nozzles, during active printing.
However, a ‘keep wet cycle’ cannot be used when the printer is left idle over long periods of time, for example, when it is in between print jobs, switched off or in transit. Furthermore, a ‘keep wet cycle’ is not appropriate for clearing severely blocked nozzles and does not address the problem of printhead face flooding. Accordingly, inkjet printers typically include a printhead maintenance station, which is designed to prevent printhead failure and/or remediate printheads to an operational condition.
One measure that has been used for preventing printhead failure is sealing the printhead, thereby preventing evaporation of water and the drying up of nozzles. Commercial inkjet printers are typically supplied with a sealing tape across the printhead, which the user removes when the printer is installed for use. The sealing tape protects the primed printhead from particulates and prevents the nozzles from drying up during transit. Sealing tape also controls flooding of ink over the printhead face.
Aside from one-time use sealing tape on new printers, sealing has also been used as a strategy for maintaining printheads in an operational condition during printing. In some commercial printers, a gasket-type sealing ring and cap engages around a perimeter of the printhead when the printer is idle. With the printhead capped in this way, evaporation of water from the nozzles is minimized, and a relatively humid atmosphere can be maintained above the nozzles, thereby minimizing the extent to which nozzles dry up.
Furthermore, gasket-type sealing rings have been combined with suction cleaning in prior art maintenance stations. A vacuum may be connected to the sealing cap and used to suck ink from the nozzles. The sealing cap minimizes nozzle drying and entrance of particulates from the atmosphere, while the suction ensures any blocked nozzles are cleared prior to printing. Hence, this type of maintenance station employs both preventative and remedial measures.
Another remedial strategy used in prior art printhead maintenance stations is a rubber squeegee. The squeegee does not act as seal; rather, it is wiped across the printhead and removes any flooded ink. Squeegee cleaning may be used immediately prior to printing, after the vacuum flush described above.
The printhead maintenance strategies described above have several shortcomings, especially in the present age of inkjet printing. Modern inkjet printers are required to have smaller drop volumes, and hence smaller nozzle openings, for high resolution photographic printing. It is also desirable to use stationary pagewidth printheads for high-speed printing, as opposed to scanning printheads. It is also desirable to reduce the overall cost of inkjet printers and incorporate them into low-powered portable devices, such as digital cameras and mobile phones.
Current printhead maintenance strategies are unable to provide inkjet printers, which meet these demands. With smaller nozzle openings (of the order of 5-20 microns), nozzle blocking due to decap becomes a serious problem. At present, the only reliable way of dealing with blocked nozzles is to use a suction pad. However, suction devices are bulky, expensive and consume large amounts of power, making them unsuitable for many inkjet applications. Furthermore, suction pads are wasteful of ink and can consume up to 0.25 ml of ink with each remediation.
Additionally, none of the prior art maintenance stations are able to provide a printhead ready for printing after a single maintenance operation. Typically, it is necessary to employ separate preventative (e.g. sealing) and remedial (e.g. suction and squeegee-cleaning) measures in order to provide a fully operational printhead. However, operations such as squeegee-cleaning are not suitable for all types of printhead, because it exerts shear stress across the printhead and can damage sensitive nozzle structures.
Therefore, it would be desirable to provide an inkjet printhead maintenance station, which combines both preventative and remedial measures. It would further be desirable to provide an inkjet printhead maintenance station, which can be fabricated at low cost and is therefore suitable for fabrication of a disposable printer. It would be further desirable to provide an inkjet printhead maintenance station, which does not significantly impact on the overall size of the printer and is therefore suitable for incorporation into handheld electronic devices. It would be further desirable to provide an inkjet printhead maintenance station, which does not impact on the overall power consumption of the printer and is therefore suitable for incorporation into battery-powered electronic devices. It would be further desirable to provide an inkjet printhead maintenance station, which does not waste large quantities of ink with each remedial operation. It would further be desirable to provide an inkjet printhead maintenance station, which cleans ink from a flooded printhead without exerting high shear stresses across the printhead.